On the internal energy at lattice polymer interfaces

Abstract

A recent lattice theory for polymer–solvent interfaces by Szleifer and Widom contains two independent energy scales. This feature is shared by several other lattice theories in the literature. It is shown that the nearest-neighbor lattice model for polymers requires that microstates be weighted only by the exchange energy Δε. All polymer–monomer interfaces on the lattice, including the melt-vacuum interface, can be made rigorously isomorphic by an appropriate rescaling of temperature. The Szleifer–Widom theory, like most theories for the interfaces of lattice polymer and solvent, contains a Flory–Huggins term for the local contribution to the spatially varying energy. A modification which incorporates more accurate expressions for the local contribution to the energy is suggested. Direct comparisons with the results of computer simulation shows that the revision offers a substantial improvement over theories with a Flory–Huggins–like local term. However, some discrepancies remain, and it is unclear whether they arise from the remaining inadequacies in the local term or from uniquely polymeric nonlocal contributions.